See Rules 7-6 through 7-11.
Also, Table 7-5 (page 61 in the 2012 Rule Book) provides a clear summary of PI, the applicable penalties, and the enforcement spot.
In this play, see 7-8a: "Pass interference restrictions (WHICH APPLY ONLY TO A LEGAL FORWARD PASS WHICH CROSSES THE NZ UNTOUCHED BY B) begin for A at the snap"; and 7-9a,b: Restrictions end for a) all eligible A players when the pass has been touched by ANY player; b) all for ineligible A players, when the pass is touched by B"
See also 2012 Case Book plays 7.5.10B and 7.5.10D.